Introducer devices are commonly utilized for inserting medical devices, such as venous access catheters, into patients. Typically, such introducer devices comprise a peel-away sheath and a hub/handle assembly which is used in conjunction with a dilator assembly to access the vein of a patient, following insertion of a needle and guidewire. In particular, procedures for introducing a catheter into a blood vessel include the cut-down method and the Seldinger technique. The Seldinger technique involves first inserting a needle through the skin of a patient and into a vein to be catheterized, inserting a guidewire through the needle and into the vein, removing the needle from the guidewire and inserting the dilator and introducer sheath over the guidewire and into the vein, simultaneously removing the dilator and guidewire from the introducer sheath, inserting a catheter through the introducer sheath and into position within the accessed vein. Following insertion of the catheter, the introducer sheaths are generally designed such that they can be peeled away from the catheter, without affecting the catheter positioning within the vein. Such introducer sheaths and assemblies are described, for example, in U.S. Pat. No. 4,772,266 to Groshong, issued Sep. 20, 1988, and U.S. Pat. No. 4,306,562 to Osborne, issued Dec. 21, 1981, each of which is incorporated by reference herein.
Problems, however, with the above-described procedure include, 1) that upon removal of the dilator and guidewire from the sheath, blood loss through the sheath can occur, and 2) that the introducer sheath provides a conduit for the introduction of air into the patient's vein, which can result in air embolism. Moreover, the risk of air embolism increases in proportion to the diameter size of the indwelling sheath, meaning that larger diameter sheaths routinely used for the placement of larger diameter catheters would increase such risk. Thus, there have been a variety of solutions proposed, which involve the incorporation of a valve in the proximal end of the introducer sheath, which would allow passage of a guidewire and dilator while simultaneously preventing blood loss or the introduction of air through the sheath. Such proposed solutions can be found, for example, in U.S. Pat. No. 5,125,904 to Lee, issued Jun. 30, 1992, U.S. Pat. No. 5,397,311 to Walker et al., issued Mar. 14, 1995, U.S. Pat. No. 6,083,207 to Heck, issued Jul. 4, 2000, each of which is incorporated by reference herein.
The aforementioned and similarly directed patents are concerned primarily with providing an elastic valve structure that provides hemostasis and the prevention of blood loss or bleed back for arterial cannulation procedures where there is significant positive blood pressure. On the other hand, with respect to venous cannulation, blood pressure is much lower and negative pressures may be involved, meaning that while prevention of blood loss is an ancillary concern, it is the prevention of air embolism that is the most crucial consideration. Thus, there exists the need for a valved sheath introducer designed for particular use for venous cannulation.